Two Borders and Coastguard officers and two Customs officers have been suspended while an investigation is carried out into an incident when five uniformed Protección Civil volunteers from the village of El Burgo drove into Gibraltar in one of the Spanish organisation's official vehicles on Sunday.
The car passed through the normal entry controls without being challenged, and it is that failure of the normal security system which has caused an outcry on the Rock.
The police went to investigate after being notified just after 5pm that the Protección Civil car had been seen driving in Gibraltar, and they found it parked in Governor's Lane.
The occupants of the vehicle were taken for questioning and were later escorted to the border. The police say they were compliant at all times.
The men claim they had gone into Gibraltar to buy cheese and chocolate and do some other shopping.